A confocal laser scanning microscope is suitable for investigating a microscopic sample. For this purpose, fluorescent markers that form connections to structures of the sample, or to elements participating in processes in the sample, are introduced into the sample. The fluorescent markers can be activated with the aid of excitation light in such a way that they are excitable to fluoresce and/or are excited to fluoresce, with the result that the structures and/or processes in the sample are made visible. Fluorescent light proceeding from the sample, which in this connection can also be referred to as “detected light,” is separated from the illumination light and directed via a detection aperture onto a detector unit.
A scanning unit causes the illumination light beam to optically scan the sample. The detected light is detected as a function of positions of the scanning unit, so that the region of the sample from which the detected light is currently deriving is known at every point in time during detection, so that an image of the sample can subsequently be created on the basis of the acquired data.
The wavelength regions of the fluorescent light depend on the fluorescent markers. In other words, different fluorescent markers light up in different colors when they are excited to fluoresce. It is known to investigate the individual fluorescent markers, and the structures of the sample and/or processes in the sample connected to them, independently of one another by illuminating the sample exclusively with illumination light from a predetermined wavelength region, so that only a specific type of fluorescent markers is excited to fluoresce; or the detected light can be filtered with the aid of a color filter in such a way that only detected light of one or a few fluorescent makers arrives at the detector unit.
DE 43 30 347 C2 discloses an apparatus for selecting and detecting at least two spectral regions of a light beam, in which apparatus a light beam is spectrally divided. The divided light beam strikes a mirror aperture that allows part of the light to pass through to a first detector unit and reflects the remainder of the light to a second detector unit.